Green Lake County, WI: EPA's radon zone, explained

Green Lake County is mapped as Zone 1 - Highest Potential by EPA — meaning the county-wide average indoor level is predicted above 4 pCi/L. Green Lake County sits at the 81st percentile nationally for radon potential — above 81 of every 100 rated counties.

Green Lake County by the numbers

Green Lake County, Wisconsin is home to about 19,370 people across 349.541 square miles. Averaged across its land area, Green Lake County runs about 55 people per square mile. By population, Green Lake County is the 586th largest of every county sharing its EPA zone — the 45th percentile by population within that zone. EPA's geology-based Region 5 groups Green Lake County with 523 other counties nationally sharing its underlying rock and soil profile.

Zone vs. an actual test

Green Lake County carries a Zone 1 label because its predicted average clears 4 pCi/L outright — three-plus times the 0.4 pCi/L typical outdoors and above the 1.3 pCi/L most homes see. A Zone 1 rating means testing is worth doing sooner rather than later, but it is still county-wide average, not a reading for any single house — some homes in Green Lake County will test well under the action level, and EPA's guidance is to test regardless of zone.

If Green Lake County tests above the action level

For a Green Lake County homeowner, the order is simple: test first, since a kit costs a small fraction of what mitigation would. Only if the result clears 4 pCi/L does a system — typically $800–$2,500, about $1,200 for a common install — become worth pricing out.

Find Wisconsin's state radon program

For Green Lake County, an ongoing number beats a one-time test - a Airthings radon monitor tracks Green Lake County's levels over time. RadonZoneCheck earns a commission there, at no extra cost to you. RADONZONE-10OFF at checkout knocks 10% off.

Where Green Lake County's figures come from

Every figure on this page traces to EPA's own Map of Radon Zones and Census data, documented in the methodology guide. Whatever zone Green Lake County carries, the zone explainer covers what it does and doesn't tell you about any one house.